As mentioned before, Godot considers that a project exists in any
given folder that contains a project.godot text file, even if such
file is empty.

Accessing project files can be done by opening any path with res://
as a base. For example, a texture located in the root of the project
folder may be opened from the following path: res://some_texture.png.

While the project is running, it is a common scenario that the
resource path will be read-only, due to it being inside a package,
self-contained executable, or system-wide install location.

Storing persistent files in such scenarios should be done by using the
user:// prefix, for example: user://game_save.txt.

On some devices (for example, mobile and consoles), this path is unique
to the project. On desktop operating systems, the engine uses the
typical ~/.local/share/godot/app_userdata/Name on macOS and Linux,
and %APPDATA%/Name on Windows. Name is taken from the
application name defined in the Project Settings, but it can be
overriden on a per-platform basis using
feature tags.